Stats

Armor, magic resist, mana and attack speed are the same at every star level.

Sejuani

1 star: Throw a giant firecracker at the closest enemy that explodes in a large circle after a 2-second delay. Enemies in the explosion take 150 magic damage and are Stunned for 2.5 seconds. ?
2 star: Throw a giant firecracker at the closest enemy that explodes in a large circle after a 2-second delay. Enemies in the explosion take 250 magic damage and are Stunned for 2.5 seconds. ?
3 star: Throw a giant firecracker at the closest enemy that explodes in a large circle after a 2-second delay. Enemies in the explosion take 1600 magic damage and are Stunned for 8 seconds. ?

5 patches changed Sejuani, read out of Riot’s game files.